This invention is directed to a method of debubbling an ink by using a membrane contactor.
It is known to use hollow fiber membrane contactors to degas liquids. See, for example, the LIQUI-CEL(copyright) SemiPer(trademark) membrane contactor commercially available from Celgard Inc. of Charlotte, N.C. This contactor utilizes a homogeneous, nonskinned, symmetric, polypropylene microporous hollow fiber membrane coated with a fluoropolymer and has been used to remove gases from photoresist developer solutions, lithographic printing plate solutions, and photographic film and paper emulsions. In this contactor, the foregoing liquids flow over the exterior surfaces of the hollow fibers.
Inks, for example, inks for ink jet printers, are sensitive to bubble formation. Formation of the bubbles, as the ink is discharged, can be detrimental to, among other things, quality printing applications or cartridge filling operations. See, for example, European Publication 1,033,163, Paragraph 0014, which is incorporated herein by reference.
Several membrane-based solutions have been proposed for bubble-in-ink problems. See, for example, Japanese Kokai""s 517712; 10-60339; 10-298470; European Publications 1,033,162; 1,052,011; and U.S. Pat. No. 6,059,405. Also, please note European Publication 1,033,162, Paragraph 0007 which categorizes additional techniques for removing dissolved gases from chemical liquids by use of a membrane.
Japanese Kokai 5-17712 discloses the use of membranes made from polyethylene, polypropylene, poly(tetrafluoroethylene), polystyrene, or polymethyl methacrylate resins (Paragraph 0008), and the ink flows on the lumen side of the membrane (Paragraph 0007).
Japanese Kokai 10-60339 discloses the use of membranes made from a fluororesin (claim 2), and the ink flows on the lumen side of the membrane (abstract).
Japanese Kokai 10-298470 (and its related case European Publication 1,052,011) discloses the use of composite (or conjugate or multi-layered) membranes with porous and nonporous layers, and suggests, among other things, the use of polymethylpentene (or PMP or poly(4-methylpentene-1)) (Paragraphs 0018-0020), and the ink flows on the lumen side of the membrane (abstract).
European Publication 1,033,162 discloses the use of composite membranes, with porous and nonporous layers and suggests, among other things, the use of PMP (Paragraphs 0026 and 0048) for both layers, and the ink flows on the lumen side of the membrane (Paragraph 0054).
U.S. Pat. No. 6,059,405 discloses the use of a membrane, a hollow fiber membrane, and the ink flows on the lumen side of the membrane (column 3, lines 55-65).
While each of the foregoing had a measured success in accomplishing the debubbling goal, there is still a need for a method of removing entrained gases from inks in a simple and cost effective manner.
The present invention is directed to a method for debubbling (or degassing) an ink. The method comprises the steps of: providing an ink having an entrained gas; providing a membrane contactor comprising a plurality of integrally asymmetric hollow fiber microporous membranes; a membrane defining within the contactor a lumen side and a shell side; providing a vacuum source; passing the gas entrained ink through the shell side of the contactor; applying the vacuum source to the lumen side of the contactor; and debubbling the gas entrained ink across the membrane.